A group of scientists at Germany’s Ludwig-Maximilians University (LMU, Munich; www.en.uni-muenchen.de) has developed a new technique to simplify the process of sorting plastics in recycling facilities. Using photoexcitation, the researchers are able to exploit the polymer-specific nature of intrinsic fluorescence. LMU’s Prof. Heinz Langhals explains, “Plastics emit fluorescent light when exposed to a brief flash of light, and the emission decays with time in a distinctive pattern. Thus, their fluorescence lifetimes are highly characteristic for the different types of polymers, and can serve as an identifying fingerprint.”

Using this technique, which is subject to a patent application, plastic particles are exposed to a flash of light, causing them to fluoresce. Photoelectric sensors then measure the intensity of the light emitted in response, which gives away the material’s dynamics of decay. Since each polymer material has a specific fluorescence lifetime, this decay curve can in fact identify their chemical nature, the LMU team explained.

Using this process, which can identify and sort up to 1.5 t of plastic per hour, would ensure less contamination in the ensuing recyclate by means of a wholly automated identification scheme, LMU said.